2. Structural Engineering
CE-407
Lec-04
Structural Engineering
Bridges-II
( ACI
By Dr. Attaullah Shah Swedish College of Engineering and Technology Wah Cantt.

3. Elevation and cross section of Bridges

4. Arch and suspension Bridges

5. Some important definitions

19. Bridges

20. Great Stone Bridge in China
History of Bridge Development
100 B.C. Romans
2,104 years ago
700 A.D. Asia
1,304 years ago
Clapper Bridge
Roman Arch Bridge
Tree trunk
Stone
Arch design
evenly distributes
stresses
Natural concrete
made from mud
and straw
Clapper Bridges employed all over the world, most notably in England. Originally, tree logs used, but they tended to rot. Stones were better, but difficult to maneuver. The Romans developed highways that connected the empire. Bridges helped them do this.
Great Stone Bridge in China
Low bridge
Shallow arch
Allows boats
and water to pass
through

21. History of Bridge Development
1900
1920
Truss Bridges
Mechanics of Design
Wood
2000
Suspension Bridges
Use of steel in suspending cables
Prestressed Concrete
Steel

22. Basic Concepts
Span - the distance between two bridge supports, whether they are columns, towers or the wall of a canyon.
Force -
Compression
Tension
Compression –
Tension -
Concrete has good compressive strength, but extremely weak tensile strength. What about steel cables?

23. Basic Concepts Beam - a rigid, usually horizontal, structural element
Pier
Pier - a vertical supporting structure, such as a pillar
Cantilever - a projecting structure supported only at one end, like a shelf bracket or a diving board
Load - weight on a structure

24. Types of Bridges
Basic Types:
Truss Bridge
Beam Bridge
Arch Bridge
Suspension Bridge
Floating Bridge
Floating
Truss
Beam
Arch
Suspension
The type of bridge used depends on the obstacle. The main feature that controls the bridge type is the size of the obstacle.

25. Truss Bridge
Typical 40m to 500m
All beams in a truss bridge are straight. Trusses are comprised of many small beams that together can support a large amount of weight and span great distances.

26. Types of Bridges
Beam Bridge
Consists of a horizontal beam supported at each end by piers. The weight of the beam pushes straight down on the piers. The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 250 feet.

27. Types of Bridges Forces
Beam Bridge
Forces
When something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulled apart.

28. Types of Bridges
Arch Bridges
The arch has great natural strength. Thousands of years ago, Romans built arches out of stone. Today, most arch bridges are made of steel or concrete, and they can span up to 800 feet.

29. Types of Bridges Forces
Arch Bridges
Forces
The arch is squeezed together, and this squeezing force is carried outward along the curve to the supports at each end. The supports, called abutments, push back on the arch and prevent the ends of the arch from spreading apart.

30. Types of Bridges
Suspension Bridges
This kind of bridges can span 2,000 to 7,000 feet -- way farther than any other type of bridge! Most suspension bridges have a truss system beneath the roadway to resist bending and twisting.

31. Types of Bridges Forces
Suspension Bridges
Forces
In all suspension bridges, the roadway hangs from massive steel cables, which are draped over two towers and secured into solid concrete blocks, called anchorages, on both ends of the bridge. The cars push down on the roadway, but because the roadway is suspended, the cables transfer the load into compression in the two towers. The two towers support most of the bridge's weight.

32. Types of Bridges Floating Bridge
Pontoon bridges are supported by floating pontoons with sufficient buoyancy to support the bridge and dynamic loads.
While pontoon bridges are usually temporary structures, some are used for long periods of time.
Permanent floating bridges are useful for traversing features lacking strong bedrock for traditional piers.
Such bridges can require a section that is elevated, or can be raised or removed, to allow ships to pass.

33. Floating Bridges
Retractable!
But high maintenance!

34. Ground below bridge Loads Materials Shapes Bridge Engineering
How do the following affect your structure?
Ground below bridge
Loads
Materials
Shapes

35. Some Uses of Bridges Walkways Highways/Roads Railways Pipelines
Connecting lands
Crossing rivers and canyons

36. Types of Bridges
Arch
Truss
Cantilever
Cable-Stayed
Suspension

43. What makes a bridge stay up?
Forces
Compression – a pushing or squeezing force
Tension – a pulling or stretching force

44. Arch Bridges
Keystone – the wedge-shaped stone of an arch that locks its parts together
Abutments – the structures that support the ends of the bridge

45. Arch Bridges
Works by
Compression

46. Arch Bridges
Where have you seen these bridges?

47. Cold Spring Arch Bridge, Santa Barbara, CA

48. Marsh Rainbow Arch, Riverton, KS

49. Pont du Gard, Nimes, France

50. Cable-Stayed Bridges Piers – the vertical supporting structures
Cables – thick steel ropes from which the decking is suspended
Decking – the supported roadway on a bridge

51. Cable-Stayed Bridges
Works by Tension AND Compression

52. Cable-Stayed Bridges
Where have you seen these bridges?

53. Zakim Bridge, Boston, MA

54. Sunshine Skyway Bridge, Tampa, FL

55. Sundial Bridge, Redding, CA

56. Suspension Bridges Similar to Cable-Stayed
Different construction method

57. Suspension Bridges
Works by Tension and Compression

58. Suspension Bridges
Where have you seen these bridges?

59. Golden Gate Bridge, San Francisco, CA

60. Brooklyn Bridge, Brooklyn, NY

61. Verrazano-Narrows Bridge, New York, NY

62. Other Types Truss Southern Pacific Railroad Bridge, Tempe, AZ
Cantilever
Firth of Forth-Forth Rail Bridge, Edinburgh, Scotland

63. FUNCTION OF A BRIDGE
Bosporus Straits Bridge
at Istanbul, Turkey –
To connect two communities which are separated by streams, valley, railroads, etc.
Replaces a slow ferry
boat trip
Connects two continent
Built in 1973
Total length is 5000 ft

64. COMPONENTS OF A BRIDGE Deck or Slab: supported roadway on abridge
Beam or Girder: A rigid, usually horizontal,
structural element
Abutment: The outermost end supports on a
bridge, which carry the load from
the deck
Pier: A vertical supporting structure, such as a
pillar
Foundation

65. COMPONENTS OF A BRIDGE
Deck
Girder
Abutment
Pier

66. TYPES OF BRIDGES Beam or Girder Bridge Truss Bridge Rigid Frame Bridge
Arch Bridge
Cable Stayed Bridge
Suspension Bridge

67. Chesapeake Bay Bridge, Virginia
GIRDER BRIDGE
Typical span length 30 to
650 ft
World’s longest: Ponte Costa
e Silva, Brazil with a center
span of 1000 ft
Chesapeake Bay Bridge, Virginia

68. Firth of Forth Bridge, Scotland
TRUSS BRIDGE
Typical span length
150 to 1500 ft
World’s longest:
Pont de Quebec, Canada
with a center span of
1800 ft
Firth of Forth Bridge, Scotland

69. RIGID FRAME BRIDGE Girders and piers act together
Cross-sections are usually I-shaped or box-shaped.
Design calculations for rigid
frame bridges are more
difficult than those of simple
girder bridges.

70. ARCH BRIDGE Larimer Avenue Bridge, Pittsburgh
After girders, arches are the second oldest bridge type.
Arches are good choices for crossing valleys and rivers
Arches can be one of
the more beautiful
bridge types.
Typical span length
130 ft – 500 ft.
World’s longest:
New River Gorge Bridge, U.S.A. with a center span of
1700 ft.
Larimer Avenue Bridge, Pittsburgh

71. CABLE STAYED BRIDGE Continuous girder with one or more towers
erected above in the
middle of the span.
From these towers
cables stretch down
diagonally and support
the girder.
Typical span length
350 to 1600 ft.
World’s largest bridge:
Tatara Bridge, Japan
center span: 2900 ft.
Normandie Bridge

72. Golden Gate Bridge, California
SUSPENSION BRIDGE
Continuous girder with one or more towers erected above in the middle of the span.
At both ends of the bridge, large anchors or counter weights are placed to hold the ends of the cables.
Typical span length
250 to 3000 ft.
Golden Gate Bridge, California

73. Factors Describe a Bridge
Four main factors are used in describing a bridge:
Span (simple, continuous, cantilever)
Material (stone, concrete, metal, etc.)
Placement of the travel surface in relation to the
structure (deck, through)
Form (beam, arch, truss, etc.).

74. Basic Span Types
Simple Span
Continuous Span
Cantilever Span

75. LOADS ON BRIDGES Permanent Loads: remain on the bridge for an
extended period of time (self weight of the bridge)
Transient Loads: loads which are not permanent
- gravity loads due to vehicular, railway and
pedestrian traffic
- lateral loads due to water and wind, ice floes,
ship collision, earthquake, etc.

76. VEHICULAR DESIGN LOADS (HL 93)
AASHTO – American Association of State Highway
and Transportation Officials
This model consists of:
Design Truck
Design Tandem
Design Lane

77. DESIGN TRUCK
145 kN
35 kN
4.3 to 9.0 m
4.3 m
9.3 N/m
DESIGN TRUCK

78. DESIGN TANDEM
110 kN
9.3 N/m
1.2 m
DESIGN TANDEM

79. DESIGN PRINCIPLES Resistance ≥ effect of the applied loads
Strength of the Member ≥ Factor of Safety x Applied Load
Allowable Stress Design (ASD):
Load and Resistance Factor Design (LRFD):
η ∑γiQi ≤ φi Rn
Where, Qi = Effect of loads
Rn = Nominal resistance
γi = Statistically based resistance factor
applied to the force effects
φi = Statistically based resistance factor applied to
the nominal resistance
η = Load modification factor

80. MATERIALS FOR BRIDGES
Concrete
Steel
Wood

81. CONCRETE BRIDGES
Raw materials of concrete: cement, fine
aggregate coarse aggregate, water
Easily available
can be designed to satisfy almost any geometric
alignment, straight to curved
can be cast-in-place or precast
Compressive strength of concrete range from
5000 psi to 8500 psi
Reinforced concrete and prestressed concrete

82. STEEL BRIDGES Minimum construction depth Rapid construction
Steel can be formed into any shape or form
Predictable life
Ease of repair and demolition

83. WOOD BRIDGES Convenient shipping to the job site
Relatively light, lowering transportation and initial
construction cost
Light, can be handled with smaller construction
equipment
Approx. 12% of the bridges in US are wood bridges
Commonly used for ft span

84. Wood Bridge on Concrete Abutments
Three Span Wood Bridge

85. GIRDER CROSS-SECTIONS COMMONLY USED IN BRIDGES

86. COLLAPSE OF BRIDGES Poor design Inadequate stability of the foundation
Fatigue cracking
Wind forces
Scour of footing
Earthquake

87. Before
Collapse
After Collapse

88. AKASHI KAIKYO BRIDGE, JAPAN
Completion Date: Cost: $4.3 billion
Length: 12,828 feet Type: Suspension
Materials: Steel Span: 6,527 feet

89. SUNSHINE SKYWAY BRIDGE, USA
Completion Date: Cost: $244 Million
Length: 29,040 feet Type: Cable Stayed
Materials: Steel, Concrete Span: 1200 feet

90. NEW RIVER GORGE BRIDGE, USA
Completion Date: Cost: $37 Million
Length: 4,224 feet Type: Arch
Materials: Steel Span: 1700 feet